The present invention relates generally to digital data and analog voice transmissions in a radiotelephone unit. More particularly, the present invention relates to the conveyance of analog voice messages by a high speed data bus between subsystems of a cellular radiotelephone with prioritized data flow of digital data messages and digitized analog messages. The present invention is related to U.S. patent application Ser. No. 732,511, "Data Transfer Method and Apparatus for Communication Between a Peripheral and a Master" filed in behalf of Paggeot et al. on the same date herewith and assigned to the same assignee.
A communication system which transmits information between two locations includes a transmitter and a receiver interconnected by a transmission channel. An information signal (which contains information, for example, an analog voice message) is transmitted by the transmitter upon the transmission channel to the receiver which receives the transmitted information signal.
Transmitters and receivers may be contained in a single apparatus so that the apparatus may both transmit and receive communications over radio-frequency channels. Cellular radiotelephones contain such transmitters and receivers together called transceivers.
The signal to be modulated may be an analog information signal (for example, a voice message) or a digital information signal (for example, an already digitized message). When the signal to be modulated is an analog signal, separate hardware signal lines are used to carry the analog signals and digital signals to the point in the transmitter where the signals are modulated. Signals are input to a cellular radiotelephone at the user interface portion of a cellular radiotelephone. Generally, devices such as microphones, keypads, or other means for inputting information signals into the radiotelephone may be contained in the user interface portion of a cellular radiotelephone, or other external devices, such as facsimile machines or external handsets, can be connected to input information to the cellular radiotelephone through a user interface to the cellular radiotelephone.
The receiver of a radio communication system which receives the modulated information signal from electromagnetic energy contains circuitry to detect, or to otherwise recreate, the information signal modulated upon the carrier signal. The process of detecting or recreating the information signal from the modulated signal is referred to as demodulation, and such circuitry for performing the demodulation is referred to as demodulation circuitry. The circuitry of the receiver is constructed to detect, and to demodulate modulated signals which have been previously modulated by a transmitter modulator.
Subsequent to demodulation, the original signal input by the user may be reconstructed, generally, after further processing of the demodulated signal is done to eliminate noise added in the transmission of the signal over the radiofrequency channel. The reconstructed signal is then output at the user interface on the receiver side of the radio system where devices such as speakers, displays, or facsimile machines may be interfaced to the radio system.
Conventional cellular radiotelephone systems require the transmitter and receiver to operate simultaneously on different radio frequencies. The signals modulated by the conventional cellular radiotelephone transmitter and demodulated by the receiver are kept separate from each other in the cellular radiotelephone unit. Newer cellular radiotelephone systems do not require the transmitter and receiver to operate simultaneously on different frequencies.
In prior cellular radiotelephone units, analog information signals were modulated and transmitted along with digital information signals, therefore, separate parallel hardware paths were generally necessary to carry the analog signals and digital signals to the modulation circuitry in order to transmit the signals. Moreover, in general, cellular radiotelephones processed analog signals as well as digital data information. The processing and transmission of the analog signals within a conventional cellular radiotelephone required additional hardware in the form of hardware signal lines and signalling hardware devices that were separate from the digital data signal lines to convey the analog signals through the cellular radiotelephone from user interface portions of radiotelephones to the transceiver. Thus, cellular radiotelephones have parallel hardware paths for analog signals and digital data signals from the user interface portion of the cellular radiotelephones to the central signal processing portion of the radiotelephones where the analog signals may be processed and digital signals properly formatted for modulation and transmission. Because a decrease in the size of radiotelephones is a desirable goal in cellular radiotelephone technology, minimization of excess hardware requires that parallel paths, such as the one between the user interface portion of a radiotelephone and the central signal processing portion, be aboided wherever possible in order to decrease the size of cellular radiotelephones.
Examples of serial digital data buses which are presently used in parallel hardware paths with analog signals may be found in a synchronous self-clocking digital data transmission system described in U.S. Pat. No. 4,369,516 to Byrns, a synchronous/asynchronous data bus system described in U.S. Pat. No. 4,972,432 to Wilson, a radiotelephone peripheral bus system described in U.S. Pat. No. 4,680,787 to Marry; and in U.S. patent application No. 5,060,264, "Radiotelephone Controller Configured for Coresident Secure and Nonsecure Modes" by Muellner et al.
The synchronous/asynchronous data bus, U.S. Pat. No. 4,972,432, described a asynchronous data transmission system layered on a slower self-clocking synchronous transmission system. The asynchronous data transmission system had much faster data transfer capability than the synchronous data transmission system described in U.S. Pat. No. 4,369,516 to Byrns. This was a particularly important characteristic when trying to integrate the functions of a portable radiotelephone with a mobile type radiotelephone peripheral to take advantage of superior mobile type characteristics, such as power output, using a minimal amount of time for the required transfer of data. An example of a mobile type radiotelephone peripheral is described in U.S. Pat. No. 4,680,787 "Portable Radiotelephone Vehicular Converter and Remote Handset", a CVC, to Marry. This integration was accomplished by splitting radiotelephone functions between the CVC peripheral and the portable radiotelephone. User variable functions were allocated to the CVC and radio functions, like call processing, were left in the portable. This required a much faster transfer of information over the cellular radiotelephone data bus in order to integrate radiotelephone functions and information between the portable radiotelephone and the CVC peripheral than possible with the synchronous data transmission invention described in U.S. Pat. No. 4,369,516 to Byrns, and the synchronous/asynchronous data transmission system, U.S. Pat. No. 4,972,432 to Wilson, met the requirement of providing greater speed for the transfer of data between the radiotelephone unit and peripheral.
Currently, there is an even greater demand for faster data transfer in cellular radiotelephones because the increased number of users on present cellular systems have strained cellular system capacity. Cellular systems require more efficient use of the resources available for cellular systems.
One manner in which cellular system capacity could be used more efficiently is to send more messages within a given period of time. This could be accomplished by digitizing all messages sent on the cellular system by cellular radiotelephones, and then sending the modulated digital messages sequentially to the individual cellular radiotelephones operating on the system. Moreover, digitizing all messages would also enable cellular systems to use the cellular system radio-frequency spectrum more efficiently because digitized analog messages use less of the radio-frequency spectrum than analog voice messages. Therefore, more digitized voice messages could be sent over a portion of the radio-frequency spectrum than the equivalent analog voice messages. One manner of doing this is to digitize the messages at the user interface to the cellular radiotelephone, and then send the messages to the central processing portion in the radiotelephone transceiver on a high speed data bus, and then to the modulation point in the transmitter. Analog messages, particularly analog voice messages, could not be digitized and sent on data buses previously used in cellular radiotelephones because the data buses were not fast enough to adequately send digitized analog voice messages, that were digitized in a real time manner, from the user interface to the transceiver portion of the cellular radiotelephone. For this reason a higher speed data bus for cellular radiotelephones is necessary.
Moreover, much higher capacity systems, such as the time division multiple access (TDMA) systems, are forcing current generation cellular radiotelephone units to process digital data and analog signals at much higher rates and to be more flexible in handling data than the aforementioned data transmission systems. In TDMA cellular radiotelephone systems, it is generally desirable that analog voice messages, which come from the user input into the radiotelephone in a continuous manner, take priority over digital data or digital control messages because the continuous nature of voice messages dictates constant sampling of the input while a voice message is being input, e.g., at a radiotelephone microphone, otherwise there will be gaps in the voice message; on the other hand, digital data coming into the radiotelephone unit is already in a form such that continuous sampling is not required because errors in routine digital data messages can be readily detected and messages can be stored and retrieved from storage and resent if an error is detected. Thus it would be desirable if a high speed cellular radiotelephone data bus accommodated analog voice messages input at the radiotelephone user interface in a real time manner, without interruption, as well as already digitized messages.
Not only are minimization of hardware and increased data transfer speed important considerations for eliminating analog signals from cellular radiotelephones, but conversion, transmission, and storage of analog voice message signals in digital form gives the cellular radiotelephone (and cellular system as well) greater flexibility and quality because once the message is in a digitally-represented form it can be stored, processed, and retrieved in a manner whereby the signal is not lost or subject to the type of signal degradation that occurs in processing, transmitting, and receiving analog signals.
Therefore, it would be desirable to provide a high speed data bus for a cellular radiotelephone that transmits data fast enough to allow the cellular radiotelephone to function in a cellular system that has greater message throughput than current cellular systems (such as a TDMA cellular system). It would also be desirable if the high speed data bus were fast enough to allow a reduction of the number of analog and digital data signals paths in the cellular radiotelephone by digitizing the analog voice message signals at the user interface portion of the cellular radiotelephone such that the same signal paths could be used to carry digital data messages as well as the digitized analog signals to other subsystems of the cellular radiotelephone as well as to peripheral devices which might be used with the cellular radiotelephone. It would also be desirable if the transmission of digital data transmitted over the high speed data bus did not cause a degradation of the digitized voice messages in a cellular radiotelephone.